Reflux extraction is a method wherein a raw material component is extracted by using a volatile organic solvent, the leaching solution is heated and distilled, wherein the volatile organic solvent is cooled after being distilled to flow back to the extractor repeatedly for extracting the raw material, and when one cycle is completed, another begins until the valuable components are thoroughly extracted. Reflux extraction is also called heat reflux extraction and is called Soxhlet extraction in laboratories. Attributing to the solid substance therein being extracted continuously by the fresh solvent, as compared with the method for extracting useful substance by a long-term soakage of the solid in the solvent, the reflux extraction not only saves solvent but also has high extraction efficiency, and its process is relatively simple, thus it is applied widely in various circumstances in which the solid-liquid extraction is required. However, the reflux extraction still requires a relatively long period of time, and because the solvent should be volatile, it is substantially limited to organic solvents.
Ultrasonic extraction realizes solid-liquid extraction separation by reducing the acting forces between the target extract and the sample matrix through rapid mechanical vibration waves generated by piezoelectric transducers. Ultrasonic cavitation is a dynamic process in which micro-gas core cavitation bubbles in liquid vibrate by the acoustic waves, and when acoustic pressure achieves a certain value, the bubbles grow and collapse. The “cavitation” and the mechanical effect generated by the ultrasonic wave in the extraction solvent result in the formation, growth, blasting and compression of bubbles in the solution in order , as to make the solid sample disperse, increase the contact area between the sample and the extraction solvent and improve the mass transfer rate of the target substance from the solid phase to the liquid phase. The ultrasonic extraction is generally conducted at a lower temperature and under normal pressure, is safe, its operation is feasible, its maintenance is convenient, and its scope of application is wide. Therefore, it is widely used in extraction of various components in Chinese medicinal materials. However, in general, the ultrasonic extraction is the batch type extraction. To extract the target in the material completely effectively, the method of adding the solvent whose volume is far larger than that of the material, or the method of multi-separation, repeated extraction is required. The former extraction method requires adding a large amount of solvent, which greatly increases the input amount and throughput of the extraction solvent; and the latter has a complex process, which greatly increases the workload.
CN201186168 and CN101306255 disclose heat reflux extraction thickener units that include an extraction tank, a filter, a heater, an evaporator, a condenser and an oil-water separator. The units can also include a demister, a vacuum and a switching tank. These units must be fed with liquid continuously and cannot be fed with material and discharge material continuously. Hence, with respect to the flowing of the material, they are batch type extraction units.
CN2401245Y discloses spiral continuous counter-flow ultrasonic wave leaching extraction equipment which is composed of a single or a plurality of cylindrical body (bodies) in which an helical propeller or spiral propeller arranged in the axial direction is provided, wherein spiral blades are densely covered with small holes, and the object of extraction is achieved by counter flow of the material and the extraction medium, and an ultrasonic transducer is arranged in parallel on an outer wall. This patent realizes the continuous extraction of the ultrasonic extraction. However, the counter flow of the material and the extraction medium can hardly be controlled. In practice, the continuous operation can hardly be realized. Furthermore, the ultrasonic transducer is arranged on the outer wall, which may cause energy loss.
CN2582599 discloses a medium separation type continuous count current ultrasonic wave natural drug extractor. As compared with CN2401245Y, this patent is a great improvement. An extraction tube of the extractor is arranged in an ultrasonic box body, the interior of the extraction tube is filled with material, and the ultrasonic box body in the exterior of the tube is sealed and filled with water, and the aqueous medium is completely isolated from the extraction solvent in the extraction tube, which can realize the counter current extraction better. Arranging an ultrasonic transducer on the outer wall of the ultrasonic box can cause energy loss. Further, the scale production can hardly be realized, because the contact between the aqueous medium and the material cannot be assured after enlargement of the scale, which cannot realize the thorough extraction of the valuable component in the material effectively.
WO 02/45812 A2 discloses an ultrasonic reflux system for one step purification of carbon nano-material, which system is composed of parts such as a condenser, an extraction tube, a solvent flask, a heat source, an ultrasonic device box, a filtering device etc., wherein the extraction tube is immersed in the box body of an ultrasonic generator, the upper side of the extraction tube is connected with the condenser, the lateral side is connected with a flask filled with the solvent by means of a siphon tube, the material can be oxidized by feeding an oxidative gas to the extractor, by means of interaction of the reflux solvent and the ultrasonic wave, the carbon nano-material can be purified. The device is a treatment device for purification in small-sized laboratories.
An ultrasonic continuous extraction device with a helical propeller has the following limitations regardless of the direction that the liquid and solid are flowing:
1. Thorough contact between the liquid and the solid cannot be assured;
2. An overlong helical propeller is not ideal because it cannot be assured that the center of the propeller moves straight forward. Such movement can damage of the equipment and cannot assure thorough leaching of the material in a single process and thereby requiring repeating the extraction process;
3. It is not suitable for solid, hard, or high viscosity material because these materials are too dense for the helical propeller.